The present invention relates to a process for energy- and emission-optimized iron production and to an installation for carrying out the process.
In smelting reduction processes for producing pig iron, a so-called generator gas, which contains CO and H2 as reducing components, is produced from carbon carriers and gas containing oxygen. The generator gas is used as a reducing gas in an assigned reduction reactor. The sponge iron produced in the reduction reactor is charged into the melter gasifier to produce liquid pig iron. Since the generator gas has too high a temperature for the processes that take place in the reduction reactor, it is cooled down to the temperature required in the reduction reactor by introducing a cooling gas. WO9733006 shows a direct reduction installation in which cooling gas is provided by cooling part of the generator gas in a gas-dust scrubber. A disadvantage of this is that large amounts of energy are given off from the generator gas into the water of the gas-dust scrubber without being used in the production of the iron.
The reduction reactor does not use up the entire content of reducing components in the reducing gas for the reduction to sponge iron, with the result that the top gas removed from the reduction reactor still has reducing power. It is known from WO9733006 to use the reducing components that remain in the top gas for producing iron in a further reduction shaft. For this purpose, a mixture of the scrubbed top gases of the reduction reactor and of the further reduction shaft are freed of the non-reducing CO2 component, heated by means of heat exchangers and post-combustion in reducing gas furnaces and, possibly after being brought together with a partial amount of the generator gas cleaned of dust, introduced into the further reduction shaft. The mixture of the scrubbed top gases of the reduction reactor and the further reduction shaft is rich in CO2, since reducing work is carried out in both reduction units. One disadvantage of this way of performing the process is the necessity for the mixture that is cool as a result of the scrubbing of the top gases to be laboriously heated to the temperature required in the further reduction shaft. Another disadvantage is the dissipation of large amounts of energy to the water of the gas-dust scrubber without being used for producing iron. Furthermore, the parts of the installation for heat exchange and for post-combustion must be designed to be large enough to cope with the amounts of gas that are fed to the further reduction shaft, which have to cover a large part of its reducing gas requirements. Correspondingly large parts of the installation are more laborious to operate and need energy to function, for example as combustible gas to be used in the reducing gas furnaces, which increases the energy consumption of the overall installation per unit of quantity of iron produced. Since the energy requirement is covered by fossil energy sources, increased energy consumption automatically also means increased CO2 emissions.